1. Field of the Invention
The present invention relates to a wet electrophotographic printer, and more particularly, to a developing unit of a wet electrophotographic printer having an improved developer supplying structure.
2. Description of the Related Art
Generally, a wet electrophotographic printer develops an image into a visible image by attaching a liquid developer on an electrostatic latent image which is formed on a photoconductive medium by a laser, and transfers the developed visible image to a printing paper to print. A developer for the wet electrophotographic printer consists of toner particles mixed with a volatile liquid carrier in a predetermined concentration, usually providing a better quality printing than a dry electrophotographic printer using a powder toner. It is also typically easier to print color images with the wet electrophotographic printer than with the dry type.
FIG. 1 schematically shows the structure of a conventional wet electrophotographic printer. As shown in FIG. 1, when a laser generated in an exposure device 10 is projected on a photoconductive drum 20, an electrostatic latent image is formed on the photoconductive drum 20. Then, a developing unit 30 develops the electrostatic latent image into a visible image by transferring the developer onto the electrostatic latent image. The developed visible image is then transferred to a transfer belt 40 and then to the printing paper P. The visible image, which is transferred onto the printing paper P, is fused onto the printing paper P while passing through a fusing unit 50.
FIG. 2 shows a conventional developing unit 30 for developing the electrostatic latent image, which is formed on the photoconductive drum 20. Referring to FIG. 2, in a cartridge 31 for storing the developer T, there is formed a partition 33 forming a developer supplying path 32 in cooperation with an inner wall 31a of the cartridge 31. At a lower part of the developer supplying path 32, a pumping roller 34 made of a sponge material is formed to contact with a lower part of the partition 33 under a predetermined pressure. As the pumping roller 34 rotates, the developer T held in the pumping roller 34 comes out from the pumping roller 34, moves up along the developer supplying path 32 and then to a deposit roller 36. The deposit roller 36 attaches the developer T onto the developing roller 37, and the developing roller 37 attaches the developer T onto the photoconductive drum 20. The developer T remaining on the developing roller 37 is removed by a cleaning roller 38.
However, in the conventional developing unit 30, the flow rate of the developer T which flows upward to the deposit roller 36 through the developer supplying path 32 varies according to various factors such as the level of the developer T of the cartridge 31, the viscosity of the developer, a pressure at which the pumping roller 34 contacts the lower part of the partition 33, and the amount of a developer sludge being wiped down by the cleaning roller 38. An irregular amount of developer T supplied into a deposit nip N between the developing roller 37 and the deposit roller 36 causes a deteriorated printing quality.
Further, in the conventional developing unit 30, the developer T from the cleaning roller 38 or the developing roller 37 is flowed into the developer supplying path 32 along the partition 33. Such developer T in a sludge form is directly supplied to the developing roller 37 with the developer T which is raised by the pumping roller 34, further deteriorating the printing quality.